<%= form.fields_for :tags do |tag_form| %>
    <div class="field">
        <%= tag_form.label :name, 'Tag:' %>
        <%= tag_form.text_field :name %>
    </div>
    <% unless tag_form.object.nil? || tag_form.object.new_record? %>
        <div class="field">
            <%= tag_form.label :_destroy, 'Remove:' %>
            <%= tag_form.check_box :_destroy %>
        </div>
    <% end %>
<% end %>